The palladium-catalyzed vinylation of organic halides provides a very convenient method for forming carbon-carbon bonds at unsubstituted vinylic positions. The reaction, reported by Heck (Palladium Reagents in Organic Syntheses, Academic Press, Canada 1985) can be used to prepare fine organics, pharmaceuticals, and specialty monomers. For example, the reaction allows a one-step synthesis of substituted styrenes from aryl bromides and is an excellent method for preparation of a wide variety of styrene derivatives. Hertz et al., Makromol Chem., 189, 119 (1968).
Vinyl toluenes have been reported as the product of a homogeneous palladium-catalyzed coupling of ethylene with bromotoluenes. R. A. DeVries et al., Organometallics, 13, 2405 (1994).
Arylation of propylene, ethylene, styrene, and methyl acrylate with iodobenzene was found to be catalyzed by metallic palladium in methanol to give methylstyrene, styrene, t-stilbene, and methyl cinnamate, respectively. Their yields and selectivities increased significantly by the addition of excess potassium acetate as an acceptor of hydriodic acid formed. Mori et al., Bull. Chem. Soc., Japan, 46, 1505 (1973).
A variety of styrene derivatives and 3-vinylpyridine were prepared in moderate to good yields by the palladium-tri-o-tolylphosphine catalyzed reaction of ethylene with aryl bromides or 3-bromopyridine, respectively. (Plevyak et al., J. Org. Chem. 43, 2454 (1978).
Alper et al. in J. Chem Soc., Chem. Comm., 1270-1271, 1983, discloses the alkenes can react with carbon monoxide, water, hydrochloric acid and a mixture of palladium and copper to produce the hydrocarboxylated branched chain carboxylic acid. Oxygen is necessary to succeed in the reaction.
Another process for preparing the branched chain carboxylic acid ibuprofen is that of Japanese Patent Application (Kokai) No. 59-10545 (Mitsubishi Petrochemical, published January, 1984), which teaches that ibuprofen can be prepared by reacting p-isobutylstyrene with carbon monoxide and water or an alcohol in the presence of a palladium(II) catalyst and a peroxide, e.g., cumyl hydroperoxide.
A new process for preparing aryl substituted aliphatic carboxylic acids or their alkyl esters is disclosed in U.S. Pat. No. 5,315,026. A 1-aryl substituted olefin is reacted with carbon monoxide in the presence of water or an alcohol at a temperature between about 25.degree. C. and about 200.degree. C. A mixture useful as a catalyst is a palladium compound and a copper compound with at least one acid-stable ligand. Ligands which may be used include include monodentate or multidentate electron-donating substances such as those containing elements P, N, O and the like, and those containing multiple bonds such as olefinic compounds. Examples of such acid-stable ligands are trihydrocarbylphosphines, including trialkyl- and triarylphosphines, such as tri-n-butyl-, tricyclohexyl-, and triphenylphosphine; lower alkyl and aryl nitriles, such as benzonitrile and n-propionitrile; ligands containing pi-electrons, such as an allyl compound or 1,5-cyclooctadiene; piperidine, piperazine, trichlorostannate(II), and acetylacetonate; and the like.
One example of a suitable ligand is an acid-stable cyclic phosphine having the formula: ##STR4## where R' is the same or different than R" and is hydrogen, alkyl or aryl, said aryl, either substituted or unsubstituted, and Ar is phenyl, naphthyl, substituted phenyl or substituted naphthyl and n is an integer from 3 to 6 is used as a catalyst. Together R', R" and the other carbon groups in the ring structure attached to phosphorous can form an aromatic ring, or naphthalene ring either substituted or unsubstituted so that the phosphine ligand can be P(Ar).sub.3 where the Ar is as defined above. Such ligands are generally known as triphenyl phosphine ligands. The term "trihydrocarbyl phosphine" is intended to mean ligands which contain one, two or three Ar groups. If less than three Ar groups are present, the balance (to provide a total of 3) is the cyclic group containing R' and R" as depicted in the formula.